Overload protection in ward leonard drive system



OVERLOAD W. R. HARRIS EIAL Filed June 21, 1951 PROTECTION IN WARD LEONARD DRIVE SYSTEM Fig.l.

G l Diesel GF 9 Engine M \l GA IO R Aux. [4 H Bus l5 l4 Fig.2.

GI GF Diesel 9 MP Engine M/\ M GA 8 A? II k Aux. I l5 4 Bus WITNESSES: INVENTORS %7% Walter R.Horris and Samuel A.Hoverstick.

Mam

ATTORNEY Patented Oct. 12, 1954 OVERLOAD PROTECTION IN WARD LEONARD DRIVE SYSTEM Walter R. Harris and Samuel A. Haverstick, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 21, 1951, Serial No. 232,807

Our invention relates to electric systems of control for dynamoelectric machines and more particularly to systems of control-for an enginegenerator set for limiting the load on the engine.

Our invention finds specialuse in marine propulsion equipment in which the main direct cur,- rent generator, supplying electric energy to the direct current propulsion motor, is coupled to and driven by a diesel engine. Since the diesel engine of a diesel-electric drive system ordinarily has no overload capacity, it is very desirable to build into the electrical portion of the system somekind of apparatus that will prevent overloading the engine.

Some devices are known in the trade for preventing excessive loadson thedrive, but so far as known to us such devices all depend solely upon the motor armature current for their intelligence. Such devices are satisfactory in that they prevent harmful overloadson the drive, but, in connection with variable voltage drives, that is, drives of the Ward-Leonard type, the devices of the prior art fall far short of perfection in that noprovision is made for variations in voltage. Consequently, at low voltages, the prior art devices overprotect the apparatus and thus do not permit the fullest utilization of the diesel engine capacity when it is most needed. Such conditions occur on marine drives during acceleration t and maneuvering when for short periods of time the motor load current may exceed rated value at less than 100% voltage. product of the instantaneous motor load current and applied voltage does ont necessarily exceed the rated power of the diesel engine. While our system of control will be disclosed in connection with diesel electric marin propulsion drives, its use is not limited to marine applications.

One broad object of our invention is to control the motor excitation of a Ward-Leonard drive as a function of the motor load current and the voltage of the generator supplying the motor.

Another broad object of our invention is the provision of controlling the power delivered to the motor of a Ward-Leonard drive as a function of the product of the motor armature current and the voltage applied to themotor armature.

A somewhat more specific object of our in-' vention is the provision of a motor excitation in a Ward-Leonard drive that is proportional to the power delivered by the motor.

It is also a broad object of our invention to vary the power output of a direct current'generator, for terminal voltages of the generator less than rated value, as a function of the product of the At such times the 4 Claims. (Cl. 318-143) terminal voltage and the generator armature current.

Other objects and advantages will become more apparent from a study of the following a specification and the accompanying drawing, in

which:

Figure 1 is a diagrammatic showing of one embodiment of our invention;

Fig. 2 is a diagrammatic showing of a modification of our invention.

In Fig. 1, the diesel engine I, is coupled to drive the main generator GI The main generator armature GA is connected in a loop circuit including the generator armature GA, lead 2, the motor series, or commutating field MSF, the motor armature MA of the motor MI, and lead 3 back to the main generator armature. The motor MI is coupled to drive the ship propeller P.

The generator field GE is excited, through the rheostat R, from the constant potential direct current buses 4 and 1. Since the drive shown is a Ward-Leonard type drive, it is apparent that the rheostat R is important in altering the speed of the motor MI by variation of the main generator voltage.

Our control includes two relatively small motor generator sets comprising motor M2 and generator G2, and motor M3 and generator G3, respectively.

The motor M2 has its armature connected directly in parallel with the circuit including the motor field MSF and the field 8 of generator G2 connected in parallel therewith, and the motor armature MAE Since the field winding 9 of the motor M2 is excited at a constant value from the constant voltage direct current busses 4 and 1, it is apparent that the speed of the generator G2 will be proportional to the voltage being suppliedto the propulsion motor Ml. Further, since the field 8 is being excited in proportion to the load current of motor Ml, it is apparent that the output voltage of generator G2 will vary with the product of the voltage and current of the propulsion motor MI, This voltage output of generator G2 We utilize to excite one of the fields of the generator G3.

The generator G3 has a self-exciting field iii connected across the armature terminals of this generator. This field It is designed and so tuned that its resistance line lies somewhat above the no-load saturation curve of generator G3. This design of field l0 and its tuning provides for a high degree of accuracy and sensitivity of our control.

The armature of the generator G2 is connected in a circuit that may be traced from the junction H on lead 4, through the field I! of the generator G3, the armature of generator G2, the copper-oxide rectifier l3, to the adjustable tap l4 on the potentiometer resistor l5, and lead 4 back to the junction ll. Tap I4 is so adjusted that the voltage of generator G2 exactly opposes a portion of the potential of the direct current buses 4 and I when 100% power is being delivered by the motor MI. When more than 100% power is being delivered by motor Ml, the output voltage of generator G2 will exceed the potential it bucks, and in consequence a corrective current will flow in the field I2 of the generator G3. The corrective current under these conditions will be such that the voltage output of generator G3 will now boost the excitation current flowing from lead 4 through the armature of the generator G3, the field MB of the motor Ml back to the other direct current bus.

When less than 100% power is being delivered by motor MI, and the output voltage of generator G2 is less than the potential it bucks, then a flow of current in the opposite direction through the field H! of generator G3 is prevented by the rectifier 13.

The modification shown in Fig. 2 is similar to the embodiment shown in Fig. 1 except that our control is applied to the generator GI. In this modification, all the elements that function in exactly the manner as shown in Fig. 1 have been designated by the same reference characters. For example, motor M3 is coupled to the con stant potential direct current buses 4 and 1, exactly as shown in Fig. 1, and thus operates at constant speed.

In this case, the output of generator G3, though functioning exactly as in the showing of Fig. l, is connected to boost the excitation of generator field GF more, or less, depending on the output of generator G3. When the power output of motor Ml rises above 100%, then the generator field GF excitation is decreased and in consequence this decreases the voltage of generator GI to thus prevent a rise of motor output above the 100% for which our control is adjusted. In case the control is effected by excitation control of the generator a rhtostat as RM in the motor field circuit may be very helpful.

While we have shown but two applications of our invention, our invention is not limited to the showings made nor the specific application discussed, but changes may be made all within the spirit of our invention.

We claim as our invention:

1. In a system of control, in combination, a load operating Ward-Leonard drive including a main generator and a main motor and in which the main generator is excited at any selected value within a given range and is operated at a substantially constant speed, a source of voltage comprising a motor operating at substantially constant speed and a generator coupled to the motor to be driven thereby, a second source of voltage comprising a motor and control generator driven thereby, said motor having its armature winding connected to the main generator and having a field winding excited as a function of the load current of the main motor, whereby the output of the control generator is a function of the product of the voltage applied to the main motor and the load current of the main motor, means responsive to the output voltage of the control generator for varying the excitation of the generator of the first named source of voltage, and circuit means for controlling the effective voltage applied to the main motor as a function of the output of the generator of the first-named source of voltage.

2. In a system of control, in combination, a Ward-Leonard drive including a main motor and a main generator excited at any selected value within a given range, and operated at a substantially constant speed, a source of voltage comprisinga motor and a control generator driven thereby, said motor having its armature connected to the armature terminals of the main generator and having a field winding excited in proportion to the load current of the main motor, whereby the output of the control generator is proportional to the product of the load current of the main motor and the voltage applied to the main motor, and means responsive to the output voltage of the control generator for controlling the effective voltage applied to the main motor.

3. In-a system of control, in combination, a Ward-Leonard drive including a main motor and a main generator excited at a selected value within a given range and operated at a'substantially constant speed, a first source of voltage comprising a motor and a control gen-- motor and having a field winding excited at aconstant value, said control generator having a field winding excited in proportion to the armature current of the main motor, whereby the voltage output of the control generator is proportional to the product of the voltage and current supplied to the main motor, an adjustable source of voltage adjustable over a selected range, a third source of voltage comprising a constant speed motor and an amplifying generator driven thereby, said amplifying generator having a field winding that is connected to the first source of voltage and the adjustable source of voltage, whereby the amplifying generator has an output that is proportional to the algebraic sum of the adjustable voltage and the output of the control generator, and circuit means for connecting the field winding of the main generator in the output circuit of the amplifying generator.

4. In a system of control, in' combination, a Ward-Leonard drive including a main motor and a main generator excited at a selected value within a given range and operated at a substantially constant speed, a first source of voltage comprising a motor and a control generator driven thereby, said motor being connected to have its armature winding energized as a function of the voltage applied to the main motor and having a field winding excited at a constant value, said control generator having a field winding excited in proportion to the armature current of the main motor, whereby the voltage output of the control generator is proportional to the product of the voltage and current supplied to the main motor, a second voltage source having a voltage of a constant selected value, a third source of voltage comprising a constant speed motor and an amplifying generator driven thereby, a rectifier, said amplifying generator having a field winding that is connected in series with the first source of voltage, the rectifier, and the second source of voltage, the first and second source of voltage being connected in bucking relation and the rectifier being so poled that excitation current flows in the mentioned field winding of the 5 amplifying generator only when the voltage of the first source of voltage is in excess of the voltage of the second source of voltage and circuit means for connecting the field winding of the main generator in the output circuit of the amplifying generator.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 591,343 Dunn Oct. 5, 1897 684,083 Moskowitz Oct. 8, 1901 Number Number Name Date Burt June 17. 1941 Miller June 16, 1942 Stoltz Oct. 6, 1942 Button Oct. 19, 1943 Edwards et a1 Apr. 18, 1944 Schaelchlin Aug. 7, 1945 Bennett Jan. 8, 1952 FOREIGN PATENTS Country Date Great Britain June 1, 1922 

